7. Local Anesthetics

Question 1

What are the two types of local anesthetics?

Answer 1

amides

esters

Question 2

how are amides metabolized?

Answer 2

by the liver

Question 3

how are esters metabolized?

Answer 3

in the blood (by pseudocholinesterase)

Question 4

what are properties for a good local anesthetic?

Answer 4

• not irritating to tissues
• no permanent damage to nerves
• low systemic toxicity
• short onset
• long DOA

Question 5

how can you differentiate btwn amides and esters based on drug name?

Answer 5

amides have 2 “I’s” in the name

Ex. lidocaine

Question 6

what is the MOA of anesthetics?

Answer 6

• inhibits excitation by increasing the threshold for depolarization
• prevents increase in permeability of mb to Na+

Question 7

know the order of function in which are blocked first to last.

Answer 7

pain- first
temp
touch
proprioception
deep pressure
movement- last

Question 8

what effect does pH have on anesthetics?

Answer 8

increasing pH (more basic) will decrease effectiveness of anesthetic because all anesthetics are slightly acidic

Question 9

what effect does epinephrine have on anesthetics?

Answer 9

• increases DOA
• decreases systemic toxicity
• provides hemostasis

Question 10

what dilution should be used for epi?

Answer 10

1:100,000

safer at 1:200,000

Question 11

how much anesthetic does 0.25% anesthetic contain?

Answer 11

2.5mg/ml or cc

Question 12

how much anesthetic does 0.50% anesthetic contain?

Answer 12

5 mg/ml

Question 13

how much anesthetic does 1.0% anesthetic contain?

Answer 13

10 mg/ml or cc

Question 14

how much anesthetic does 2.0% anesthetic contain?

Answer 14

20mg/ml or cc

Question 15

how many mg of each anesthetic are contained in 10cc of a 50/50 mixture of 2% lidocaine and 0.50% marcaine?

Answer 15

5cc of 2% lidocaine –> 20x 5= 100 mg lidocaine

5cc of 0.50% marcaine –> 5x5= 25 mg marcaine

Question 16

what is the toxic dose of lidocaine (plain)?

Answer 16

300mg

Question 17

what is the toxic dose of lidocaine w/ epi?

Answer 17

500 mg

Question 18

what is the toxic dose of marcaine, plain?

Answer 18

175 mg

Question 19

what is the toxic dose of marcaine, with epinephrine?

Answer 19

225 mg

Question 20

how many cc of 2% lidocaine, w/ epi can be given before the toxic dose is reached?

Answer 20

500 mg (toxic dose)/ 20 mg= 25mg

Question 21

what is the advantage of bupivicaine over lidocaine?

Answer 21

longer DOA (6-8 hrs) compared to lidocaine (3-4 hrs)

Question 22

what is the advantage of mixing anesthetics?

Answer 22

quicker onset and longer duration of action

Question 23

hypersensitivity is usually related to which type of anesthetic?

Answer 23

esters (and related compounds)

Question 24

hypersensitivity to amide is usually related to what?

Answer 24

preservatives in the anesthetic

Question 25

what are some ways to make injections less painful?

Answer 25

- warm anesthetic - smaller needle - right size syringe - topical refrigerants - add sodium bicarbonate

Question 26

what is the ring block?

Answer 26

specific nerve block in the hallux used for bunion surgery

Question 27

what are the different types of hallux blocks?

Answer 27

``` 2-point injection V block Infiltration H-block ring block triangle block ```

Question 28

which nerves are blocked in an ankle block?

Answer 28

1. tibial nerve 2. saphenous nerve 3. superficial peroneal nerve (medial and intermediate dorsal cutaneous n.) 4. sural nerve 5. deep peroneal nerve

Question 29

where would you do the deep peroneal nerve block?

Answer 29

inject btwn the EDL and EHL, just lateral to the anterior tibial artery